Treatment of sulphite pulp and liquor



T. L. DUNBAR TREATMENT OF SULPHITE PULP AND LIQUOR April 17, 1934, I

Filed April 13, 1932 lNl/ENTOR A ITTORNEV where.

Patented Apr. 17, 1934 1,955.05: TREATMENT or smm'm rum AND mouoa Thomas Leonidas Dunbar, Watelitown, N. Y.

Application April 13, 1932, Serial No'. 605,033

25 Claims.

The present invention relates to a method and apparatus for the treatment and washing of sulphite pulp and to the recovery of gasesand heat at the completion of the cook.

In the digestion of fibrous material by the sulphite process, the completion of the cook leaves the digester charged with pulp and acid liquor at an average temperature in the neighborhood of 290? F. A purer product can be obtained if the cooked pulp is washed with water. While cold water may be used to wash cheaper grades If the pulp is washed in the digester, has been proposed in the soda process, the treatment has heretofore been subject to the same disadvantage.

In addition, the average sulphite digester is normally blown with the liquid having an S0: content of close to 6%. When this liquor is run to waste there is thus a large loss of S02.

An object of my invention is the provision of improvement in the method and apparatus for the treatment of sulphite pulp and liquors whereby economies in operation may be effected and the efliciency of operation and the purity of the product may be increased. The invention provides matreial improvements in methods and apparatus for recovering the .gases and heat in the digester liquor at the end of the cook and for washing the pulp with warm water.

The accompanying drawing shows in diagrammatic elevation apparatus forming a part of the present invention, certain parts being omitted for thesake of clearness.

In the drawing, 1 is the digester. 2 is a strainer in the bottom of the digester for separating the liquor from the pulp mass.

Although this strainer is shown as only partially occupying the circumferential surface of the bottom cone of the digester, the exact size of the strainer will be dependent upon the digester size and in some instances it may occupy all of the bottom cone of the digester.

having a total thickness of a few inches.

The

back side of the strainer has no holes in it where it rests against the brick, but the front or inner surface next to the pulp mass has perforations.

3 is a valve in the line 4, which line carries the digester liquors from the-strainer 2 to the degassing tank 5. The series of baflles 6 is located between the degassing tank 5 and the exchange heater 7. The overflow pipe 8 is provided for carrying the degassed liquors away from the exchange heater. It will be noted that by reason of the overflow pipe 8 being brought over and down to a point near the bottom of the exchange heater tank, it will take off the cold liquor from the bottom of this tank. A valve 9 is provided in the pipe 8. The line 10 having therein the valve 11 joins the overflow pipe for the purpose of supplying wash water when it is desired to flush out the exchange heater tank. Means such as the pipe 40 may be provided for supplying gas under pressure (for example a jet of S02 gas, steam or I air) to the liquor in the chamber of the exchange heater 7 to agitate this liquor, or other means for agitation may be provided.

The water supply line 12, provided with the valve 13, leads to the exchange heater coils 14. 15 is the warm or hot water line leading from the exchange heater coils to the top of the digester, this line being provided with the valves 16 and 39 and the check valve 1'7. The line 18 leads to the hot well (not shown) and is provided with the valve 19 so that the heated water can be sent to the hot well if desired. The line 18 may also be provided with a selecting device (not shown) such as is known to the trade so that the hot water can be sent to the sewer if for any reason it should be contaminated with acid liquors.

Ordinarily the valve 13 is left open and the supply of heated water for washing the pulp in the digester is regulated by means of the valve 16. The primary purpose of the valve 13 is to shut off all water supply in case it should become necessary to make any repairs beyond that point in the exchange heater or in the line 15.

The outlet 41 connects with the branch 25 having therein the valve 26, which leads to the sewer. The outlet 41 also connects with the line 20 having therein the valve 21. The line 20 leads to the suction side of the pump 22, which discharges through the valve 23 and the line 24 into the line 5 15. Thus if it should be desired to send all of the heated water to the hot well, the cooled liquor from the digester can be returned to the digester for flushing the same out. To accomplish this, the

valve9 in the line 8 and the valve 26 in the line 25 are closed and the valve 21 is opened.- The pump 22 is started up and the valves 23 and 16 are opened. The cooled liquor from the exchange heater tank is thus returned again to the digester for flushing the contents thereof into the blow pit, where the liquor may be drained away in the usualmanner and the pulp washed.

If necessary, it is thus possible to save time of cooling the liquor drawn oil from the digester, to return said liquor to the digester and to empty the contents of the digester together with said liquor into the blow pit. The heated water from the coils 14 can then be piped to the hot well through the line 18, by closing the valve 39 and opening the valve 19, or if preferred the line 18 can have a branch leadingto the blow pit so that the stock can be washed therein with this hot water. In this last case, a hot water storage tank would be installed in this branch leading to the blow pit. These last connections are not shown on the drawing because it is believed that they do not require illustration in the light of the above description.

The cooled liquor from the exchange heater 7 can be dicharged to the sewer by means of the valve 26 and line 25 as well as by means of the pipe 8. In case it is desired to wash out the exchange heater tank, wash water may be admitted through the valve 11 and line 10 2 1d discharged to the sewer by closing the valve 21 and opening the valve 26.

The digester 1 is provided with a gauge glass 2'7 for observing the height of the liquor therein. The valves 28 and 29 are provided in the leads to the gauge glass for the purpose of shutting off the liquor from the gauge glass if repairs to the gauge glass become necessary.

The gas line 30 leads from the top of the degassing tank 5 to the eductor 31. The line 30 is provided with the branch 32 which leads to the gas cooler or gas washer ordinarily in use in bisulphite of lime acid-making systems. The valves 33 and 34 in the lines 30 and 32 respectively, control the passage of the gas from the degassing tank either to the gas cooler or gas washer by means of the branch 32 or to the eductor 31. The line 35, provided with the check valve 36, leads from the acid settling tank (not shown) to the eductor 31. The eductor 31 is of the type shown and described in the co-pending application of T. L. Dunbar and A. D. Merrill, Serial No. 528,696 filed April 8, 1931, now Patent No. 1,888,632 dated November 22, 1932. The drop leg 37 leads from the eductor 31 to the acid storage tank 38.

In the practice of my invention, the operation may be as follows:

When it has been determined that the cook has been completed in the digester, the valves 3, 13, 39 and 16 are opened. The pressure in the digester forces the liquid contents of the digester through the strainer 2, valve 3 and line 4 into the degassing tank 5. This separation of the liquor from the pulp facilitates the subsequent treatment ofthe liquor for the liberation of gases and the recovery of heat therefrom. The degassing tank 5 may be under a partial vacuum due to the flow of liquor through the line 35 and the eductor 31. Since the liquor coming from the digester is hot, its S02 content is liberated under the conditions in the degassing tank. This liberated S02 gas may be recovered either by passing it to the storage tank 38 through the eductor 31 or by passing it through the branch 32 to the gas cooler or gas washer.

The hot liquor from the digester drops through the banies 6 into the exchange heater 7. Agitation of the liquor in the exchange heater chamber, as for example by means of a jet of gas or air under pressure through the pipe 40, may also be utilized to promote the liberation of $0: from said liquor. The slight pressure thus obtained will force this liberated $02 up through the baflles 6 and chamber 5 and through the pipe 30.

The water or other liquid flowing through the exchange heater coils 14 is heated by the hot digester liquor. The liquor may then overflow through the pipe 8 to the sewer.

During the time that the liquor: is flowing through the degassing chamber, the baflles and the exchange heater, the valve 16 is open so that an equal amount of warm water is supplied to the top of the digester from the exchange heater coils 14. Or an equal amount of wash liquid may be supplied from any other source. This water or liquid follows through the digester and by displacement washes the pulp in the digester. As soon as the stock has been washed to the desired point and water appears in the overflow 8, the washing is stopped and the pulp is discharged from the digester.

Instead of the cooled digester liquor in the tank of the exchange heater 7 overflowing to the sewer through the pipe 8, it may, as previously stated, he passed through the lines 20 and 24 back into the top of the digester. In this case, the heated water from the exchange heater coils may be passed through the line 18 to the hot well, or to the blow pit, as stated above. The water from the hot well may, if desired, be utilized for making steam, thus reducing the cost of generating the necessary steam.

The exchange heater tank may be washed out by closing the valve 9 and admitting wash water through the line 10 and valve 11 into the pipe 8 and thence to the exchange heater tank. The outlet 41, valve 26 and line 25 permit draining off of the liquor in the exchange heater tank when it is desired so to wash out this tank.

Instead of pure water, another wash liquid such as a solution of chemicals suitable for washing the pulp could of course be passed through the line 15 for washing the contents of the digester.

A normal 10-ton digester will contain at the completion of the cook very nearly 200,000 pounds of liquor at an average temperature of 290 F. This liquor will contain an average of 58,000,000 B. t. u., and with my improved method and apparatus the greater part of this heat is utilized.

The average sulphite digester is normally blown with the liquor having a content of close to of S02 gas. A l0-ton digester containing 200,000

pounds of so-called spent liquor therefore contains 600 pounds of S02 gas. This 600 pounds of SO: gas is equivalent to 300 pounds of sulphur for a 10-ton digester, and my improved method and apparatus recover this valuable constituent of the spent liquor.

My invention therefore not only makes possible the production of a purer and higher quality sulphite pulp, but it also efiects large savings in heat units and in $02.

exchange heater.

2. Apparatus as described in claim 1 in which the degassing apparatus comprises a chamber and a series of battle plates. 1

3. Apparatus as described in claim 1 including means for recovering S02 gas and means for conducting gases from the degassing apparatus to such recovery means.

4. In apparatus of the character described, a digester, an exchange heater and degassing apparatus communicating with said exchange heater, and conduits for conducting acid liquor from the bottom part of the digester to the degassing apparatus and from the exchange heater to the top part of the digester.

5. Apparatus as described in claim 4 in which the degassing apparatus comprises a chamber and a series of baiiie plates.

6. Apparatus as described in claim 4 including means for recovering S02 gas and means for conducting gas from the degassing apparatus to such recovery means.

'7. In apparatus of the character described, a digester, an exchange heater and degassing apparatus communicating with said exchange heater, conduits for acid liquor connecting the lower part of the digester with the degassing apparatus and connecting the exchange heater with the top part 'of the digester, and conduits for wash liquid connecting the exchange heater with a source of supply of wash liquid and connecting the exchange heater with the digester.

8. Apparatus as described in claim '7 including a storage receptacle and means for conducting wash liquid from the exchange heater to said storage receptacle.

9. In apparatus of the character described, a digester, an exchange heater and degassing apparatus communicating with said exchange heater, a conduit for conducting acid liquor from the digester to the degassing apparatus and conduits for conducting other liquid to and from the 10. Apparatus as described in claim 9 in which the degassing apparatus comprises a chamber and a series of baflie plates.

11. Apparatus as described in claim 9, including means ior absorbing gas in a liquid and means for conducting gases from the degassing apparatus to such absorption means.

- 12. Apparatus as described in claim 9, including means for forcing gas under pressure into the exchange heater chamber.

13. Apparatus as described in claim 9, including a conduit for withdrawing spent acid liquor from the bottom part of the exchange heater chamber and conducting it out of said chamber near the top thereof, a conduit for conducting such liquor back to the topper-t of the digester, and a conduit for discharging such liquor to waste.

14. In a process of the character described, digesting fibrous material in acid liquor, separating acid liquor from said material, then treating the separated digester liquor to liberate 80: gas

and utilizing the hot degassed digester liquor to heat another liquid.

16. In a process of the character described, withdrawing hot acid liquor from the pulp in a digester, treating said liquor to liberate S02 gas therefrom, absorbing said liberated gas, utilizing the hot digester liquor to heat another liquid, discharging the pulp from the digester into a blow pit and washing the pulp therein.

17. In a process of they character described,

withdrawing hot acid liquor from the pulp in a digester, treating said liquor to liberate S02 gas therefrom, absorbing said liberated gas, returning the liquor to the digester and flushing out the contents of the digester'therewith.

18. In a process of the character described, withdrawing hot acid liquor from the pulp in a digester, conducting said liquor directly to degassing apparatus, and simultaneously liberating S02 gas from said liquor, utilizing the degassed liquor to heat washliquid and washing the pulp in the digester with the heated wash liquid.

19. Apparatus as described in claim 9, including means for absorbing S02 gas in a liquid, said absorption means comprising an eductor and a drop leg, and means for conducting gases from the degassing apparatus to such absorption means.

20. In a process of the character described, digesting fibrous material in acid liquor, separating acid liquor from said material, then treating the separated liquor to liberate S02 gas therefrom by spreading the liquor in thin layers and subjecting it to agitation, and recovering the liberate'd gas by absorbing it in liquid.

21. In a process of the character described, digesting fibrous material in acid liquor, separating acid liquor from said material, then treating the separated liquor to liberate SO: gas therefrom by subjecting the liquor to reduced pressure and spreading it in thin layers, and recovering the liberated gas by absorbing it in liquid.

spreading it in a plurality of relatively thin layers. 24'. In a process of the character described, digesting fibrous material in acid liquor, separating acid liquor from said material, treating the separated liquor to liberate SO: gas therefrom by subjecting it to reduced pressure, spreading it in thin layers, and then collecting the liquor and subjecting it to agitation.

25. In a process of the character described, digesting fibrous material in acid liquor, separating acid liquor from said material, treating the separated liquor to liberate S0: gas therefrom by subjecting it to reduced pressure and spreading it in thin layers, then collecting the liquo iand utilizing it to heat another liquid.

THOMAS LEONIDAS DUNBAR. 

